1998 Volume 71 Issue 11 Pages 783-804
Quaternary fluvial terraces are well developed along the Katashina River in north Kanto, central Japan. The author investigated them in order to clarify the influence of the Akagi volcano on the geo-morphic development of fluvial terraces since the middle Pleistocene. The results are summarized as follows:
(1) Fluvial terraces along the Katashina River can be classified into the Toyama (To), Numata (Nu), Okkai (Ok), Ikan (Ik), Hiraide (Hi), Kainose-I -III (Ka-I-III), and Low (L) surfaces, in descend-ing order. They are dated at the middle Pleistocene, 150-100ka, 110-100ka, 60ka, 50ka, 30-15ka, and 13-10ka in age, respectively.
(2) To-Ok surfaces are accumulation terrace surfaces that developed under the influences of vol-canic activities of the Akagi volcano during the middle Pleistocene.
(3) The Ik terrace deposit is correlative with the valley filling deposits that occurred in the middle and upper courses of main rivers in central Japan. The Ik surface is a climatic accumulation terrace surface.
(4) Akagi andesite gravel dominates in the Nu terrace deposit, which indicates that the develop-ment of this terrace was greatly affected by Akagi volcano activities.
(5) The rate of andesite gravel accumulation derived from the Akagi volcano has decreased gradu-ally since the accumulation period of the Ik terrace deposit. The rate was less than 30% in the Kai-nose I deposit.
(6) The changes in lithology of terrace gravel agree with the fact that volcanism has been less vigor-ous since ca. 100ka in comparison with that of the preceding period.
(7) The volcano only slightly affects the gravel layer of the present riverbed.
